Albinism and Low Vision

What Is Albinism?

Albinism represents a group of conditions characterized by a defect in the production of the pigment melanin, normally found in skin, eyes, and hair.

Any one of a number of genes responsible for the production of melanin can lead to albinism. There are two major types of albinism:

Oculocutaneous Albinism

Is inherited in an autosomal recessive fashion. This means that both copies of the gene must be abnormal (one inherited from each parent) in order to manifest the disease.

Having only one abnormal gene results in "gene carrier" status, which means that the individual does not manifest the disease.

In oculocutaneous albinism, there is little to no pigmentation/coloring of the skin, hair, and eyes.

Ocular Albinism

Is inherited in an "X-linked" fashion.

Females carry two X chromosomes, while males carry one X chromosome and one Y chromosome.

Therefore, this disease affects primarily men, who need only one X chromosome with the albinism gene to manifest the disease. Females with the albinism gene on one of their two X chromosomes may be "gene carriers" of the condition.

Unlike oculocutaneous albinism, which affects the skin, hair, and eyes, ocular albinism affects primarily the eyes. The skin and hair may be only slightly less pigmented than unaffected siblings.

How Does Albinism Affect the Eyes?

Albinism can affect the eyes in multiple ways, and individuals with albinism can vary significantly in how much their eyes and vision are affected:

People who have albinism have little to no pigmentation of the iris. They also lack pigment in the "retinal pigment epithelial" cells that lie between the retina and the choroid. This gives a unique appearance to the retina and makes the underlying blood vessels of the choroid more visible.

A normal retina with no signs of albinism.Source: Courtesy Mrinali Patel Gupta, M.D.,Weill Cornell Medical College, New York

A retina displaying signs of albinism. The lack of pigmentation makes thevessels of the choroid more visible and the retinal vessels have an abnormal course.Source: Courtesy Mrinali Patel Gupta, M.D.,Weill Cornell Medical College, New York

Since pigment in the eye absorbs light and helps us tolerate most kinds of bright light, the lack of pigment in these structures makes individuals with albinism very sensitive to light, called photosensitivity.

People with albinism also have an underdeveloped fovea. The fovea is the part of the retina responsible for much of visual acuity. This is usually the abnormality that most affects vision in ocular albinism and oculocutaneous albinism. Depending on the degree of foveal underdevelopment, vision may be mildly or severely impaired. The following photos were taken using optical coherence tomography (OCT), which is a type of medical imaging technology that produces high-resolution cross-sectional and three-dimensional images of the retina and its supporting layers:

In comparison, the normal foveal contour exhibits a dip as shown above.The foveal contour and integrity are important for high acuity vision. Source:Courtesy Mrinali Patel Gupta, M.D., Weill Cornell Medical College, New York

In addition, people with albinism may have misrouting of the visual pathways connecting the eye to the part of the brain responsible for vision. "Misrouting" means that the nerve signals traveling from the retina to the brain do not follow the usual eye-to-brain pathway.

These abnormalities result in decreased best-corrected visual acuity, ranging from 20/40 to 20/200. Albinism is non-progressive and visual acuity may improve somewhat until mid-teens, after which it remains fairly stable, unless additional eye conditions develop.

Infants with albinism also frequently exhibit abnormal, involuntary, rapid side-to-side or up-and-down movements of the eyes called nystagmus, as well as abnormalities in the alignment of the eyes called strabismus. The nystagmus often improves over time and, in some cases, may even disappear.

Both nystagmus and strabismus can impede vision. In addition, nystagmus and strabismus can cause the individual with albinism to hold or tilt his or her head in an unusual way in order to see objects or surroundings as clearly as possible.

Female carriers for the ocular albinism gene (i.e., females in whom only one of their two X chromosomes carry the disease-causing gene) may exhibit abnormal retinal pigmentation and mildly decreased iris pigmentation. Rarely, female carriers can be affected more severely and exhibit some of the findings described previously.

Is Albinism Associated with Other Medical Conditions?

There are two forms of oculocutaneous (autosomal recessive) albinism (see above) that are associated with systemic medical disease:

Chediak-Higashi Syndrome:

In addition to albinism, individuals with this syndrome exhibit abnormalities in white blood cells of the immune system and are predisposed to infections. They may also have peripheral neuropathy, an abnormality in the peripheral nerves that may cause decreased sensation, or abnormal sensations such as burning or tingling. Peripheral nerves transmit signals from the spinal cord to the rest of the body.

Hermansky-Pudlak Syndrome:

In addition to albinism, individuals with this syndrome have an abnormality in platelets (the components of blood that help create blood clots and stop bleeding), which predisposes them to bleeding. These individuals also accumulate a substance within various cells of the body, called a ceroid, which can lead to abnormalities in the lungs, intestines, and other organs.

Both conditions have significant implications on the overall health of the patient; therefore, it is important to consider these systemic conditions when a diagnosis of oculocutaneous albinism is made.

How Is Albinism Treated?

There is no cure for albinism, but a variety of measures can be taken to address some effects of the disease:

Contact lenses with a colored component overlying the part of the contact lens that sits over the iris can help block light entry into the eye to reduce light sensitivity as well. These contact lenses also address the refractive error.

Glasses with prisms can decrease nystagmus and treat strabismus (ocular misaslignment); i.e., help both eyes point or look in the same direction. Prisms are special glasses that bend light and can help redirect the direction of light entering a misaligned eye.

Surgery may also be considered to reduce nystagmus or to align the eyes (i.e. treat strabismus), especially if either is causing a significant abnormality in head position. These surgeries involve adjusting the length or position of the muscles that sit on the outside of the eye to maintain eye position and to move the eye in various directions.

Genetic counseling can help parents and adult patients with albinism understand the cause and understand the risks of the condition for future children.

Because of the decreased skin pigmentation that accompanies albinism, individuals should use wide-brimmed hats, visors, and sunscreen, and avoid excessive sun exposure in order to protect the skin from sunburn and skin cancer.

Emerging therapies: Studies in animal models of the condition have shown promise for gene therapy, in which the abnormal gene is replaced with a normal copy of the gene and results in reversal of some of the retinal abnormalities. Although this has not yet been well evaluated in humans, these animal studies suggest future potential for gene therapy for albinism.

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